Steels rolled in a rolling shop generally grow in length from tens to hundreds of meters. The rolled steel product is cut to appropriate lengths and cooled for transferring to a subsequent cooling process. Some of the cooled and cut products are again cut and straightened on an off-line assembly, but in modern rolling factories, after having been cooled, most of the products are straightened on a following in-line assembly, and are cut to required lengths.
FIGS. 6 and 7 show conventional procedures most ordinarily used, where the product from a rolling mill 1 is cut to appropriate lengths by a dividing shear 2 and is cooled by a cooling hearth 3. In the process shown in FIG. 6, a product having the length of the cooling hearth 3 is straightened by a straightener 4, and is cut by a cutter 6 to required lengths. In the process shown in FIG. 7, after having been cut by the cutter 6, the product is straightened by the straightener 4. In each of FIGS. 6 and 7 the straightener 4 and the cutter 6 are "off-line".
In either procedure, there is provided, without exception, a delay table 5 for once pooling or stopping the product between the straightener 4 and the cutting machine 6. A large space is required for installing the delay tables, and since they are positioned separate from the rest of the apparatus, they hinder operations and the saving of energy. Moreover, taking into consideration problems involved with the existing practices from the point of view of capacity, the rolling capacity must in principle match the capacity of installations after (i.e. downstream of) the cooling hearth. However, the rolling speed is 10 m/sec or more, but the straightening speed is 3 to 4 m/sec at the most, and the feeding speed in the cutting process is in general 2 m/sec. For solving imbalance in capacity the straightening and the cutting have utilized multi-treatments where a plurality of products are dealt with concurrently.
On the other hand, in cutting a plurality of bars, it is generally practised that these bars are made to collide with a gauge stopper 7a before cutting as shown in FIG. 8, so that the products which would be fed at random on the roller are set within cutting tolerance. FIG. 9(a) shows the speed pattern used for avoiding large shocks. In the speed pattern of FIG. 9(a) the products to be cut are made to slow down or stop before striking the stopper; they are fed bit by bit and are caused to strike moderately against the stopper several times, and thereafter they are cut. A cutting cycle (t1 sec) in this case is longer by (t.sub.1 -t.sub.2)sec in comparison with a cutting cycle (t2 sec) when the products are sent by the theoretical speed pattern of FIG. 9(b). In general, calculation of cutting ability is expressed by the following equation EQU Q=3600/(nt+t3).times.w.times.n.times.l.times.N.times.10.sup.-3 (T/H)
Herein;
w: Weight per unit length (Kg/m) of a single steel product PA1 l: Cut length (m) PA1 N: Number of pieces which are simultaneously cut PA1 n: Number of times cut PA1 t: Cycle time (sec) of cutting into lengths l, corresponding to t1 and t2 of FIGS. 9(a) and (b) PA1 t3: Time required to set the products before cutting, and time required to deal with scraps after cutting.
If t1 and t2 of FIGS. 9(a) and (b) are substituted into "t" of the above equation and their abilities are compared, the ability by the actual speed pattern is apparently delayed as compared with that of the theoretical speed pattern. This delayed degree depends upon factors of the cutting times (n), the cutting length (l) and others. If the degree is calculated by trial with l=5 to 6 m which is highest in production ratio, the degree is around 60 to 70%, and the ability is not heightened, notwithstanding the multi-bars cutting, and this practice often hinders productivity of the steel bar rolling line.
The present invention has been developed to solve the above mentioned problems, whereby the lay-out of the operation in the rolling line is changed completely by abolishing the step of evening up the leading ends of the products (or rods or bars) to be cut. When a plurality of products are treated in this way the productivity of the multirod rolling line is heightened.